With the result, Union Berlin move up to third place in the standings, while Mainz stay 17th after suffering their third straight defeat of the new season.
"We inflicted great pressure on our opponents throughout the game. Offensively we played inside out and showed our level," Inner Mongolia coach Zheng Wei reflected.
As expected, there was no place for striker Edinson Cavani, who has yet to find a new club after leaving Paris Saint-Germain in June. The 33-year-old has not played since March.
The host squandered a promising chance after Axel Witsel failed to make the most out of Reyna's cutback pass into the penalty area.
Jorginho scored two penalties in the 78th and 82nd minutes to assure a comfortable win in the best performance by Frank Lampard's side this season.
Earlier on Friday, Jiangsu defeated Shanghai 3-0 (25-17, 25-20, 26-24) in the third-place match.
Dilana took center stage early on by scoring seven points in a row, while Yang Shuyu provided much-needed help beyond the arc. The duo combined for 17 points in the first quarter to propel Dongguan to a 22-13 advantage.
Struber joins the Red Bulls from English Championship side Barnsley, where he's been since November 2019. The Red Bulls paid an undisclosed fee to Barnsley to release him from his contract.
The injury means that Alba will be forced to pull out of the Spanish national team squad for the forthcoming friendly game in Portugal and the UEFA Nations League ties against Switzerland and Ukraine.
Jiangsu showed its well-balanced, attacking firepower, with seven players scoring in double figures, led by Sun Li's 18.
In women's actions, top seed Simona Halep took sweet revenge on her opponent from last year's French Open defeat, trouncing American teenager Amanda Anisimova 6-0, 6-1 to progress.